Preeclampsia, a dangerous condition related to high blood pressure and protein in the urine in the later weeks of pregnancy, affects about 5 percent of pregnancies.

"What would otherwise have been considered clinically unimportant or minor 'snoring' likely has major effects on the blood supply to the fetus, and that fetus in turn protects itself by reducing movements," study principal investigator Colin Sullivan said in a news release from the American Academy of Sleep Medicine. "This can be treated with readily available positive airway pressure therapy and suggests that measurement of fetal activity during a mother's sleep may be an important and practical method of assessing fetal well-being."

The researchers focused on 20 women with moderate to severe preeclampsia whose fetuses showed much less activity overnight. Fetal activity in the womb is thought to be an indication of their health.

On alternate nights, the women received treatment with a continuous positive airway pressure (CPAP) machine designed to keep the throat open. The throat closes as many as dozens of times a night in people with sleep apnea, causing breathing to fail and waking them up without their knowledge. This leads to poor sleep and can affect adults' health.

In the study, fetal movements grew from 319 per night on average when mothers did not receive CPAP treatment to 592 movements when mothers did receive CPAP.

"Maternal [sleep-disordered breathing] represents a unique opportunity to study the effect of in utero exposures on postnatal development and future risk. This has major implications for public health," Louise O'Brien, an associate professor at the University of Michigan, wrote in a commentary on the study. "It raises the possibility that a simple, noninvasive therapy for [sleep-disordered breathing] may improve fetal well-being."

Although the study, which appears in the January issue of the journal Sleep, found an association between mothers' sleep-breathing problems and fetal movement, it did not prove a cause-and-effect relationship.